Richtek RT8452GQW, RT8452GS Schematic [ru]
Conceptual
RT8452
High Voltage High Current LED Driver Controller for Boost
or Buck-Boost Topology
General Description
The RT8452 is a current mode PWM controller designed
to drive an external MOSFET for high current LED
applications. With a current sense amplifier threshold of
180mV, the LED current is programmable with one
external current sense resistor and the power loss is
minimized. With the maximum operating input voltage of
40V and output voltage up to 60V, the RT8452 is ideal for
boost or buck-boost operation. (See RT8450 and RT8451
for buck mode LED driver application.)
With 1MHz operating frequency, the external inductor and
capacitors can be small while mainteining high efficiency.
Dimming can be either analog or PWM digital. The unique
built-in clampping comparator and filter allow easy low
noise analog dimming conversion from PWM signal with
only one external capacitor. PWM dimming control is made
easy with a build in FET driver dedicated for the extermal
dimming MOSFET.
The RT8452 is available in WQFN-16L 3x3 and SOP-16
packages.
Features
l High Voltage Capability : V
60V
l Boost or Buck-Boost Operation
l Current Mode PWM with 1MHz Switching
Frenquency
l Easy Dimming : Analog, PWM Digital or PWM
Converting to Analog with One External Capacitor
l Programmable Soft Start to Avoid Inrush Current
l Programmable Over Voltage Protection to Limit
Output Voltage
l V
Undervoltage Lockout and Thermal Shutdown
IN
l 16-Lead WDFN and SOP Packages.
l RoHS Compliant and 100% Lead (Pb)-Free
Up to 40V, V
IN
OUT
Up to
Applications
l General Industrial High Power LED Lighting
l Desk Lights and Room Lighting
l Building and Street Lighting
l Industrial Display Backlight
Ordering Information
RT8452
Package Type
S : SOP-16
QW : WDFN-16L 3x3 (W-Type)
Operating Temperature Range
G : Green (Halogen Free with Commer cial Standard)
Note :
Richtek Green products are :
}RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
}Suitable for use in SnPb or Pb-free soldering processes.
}100% matte tin (Sn) plating.
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area, otherwise visit our website for detail.
Pin Configurations
(TOP VIEW)
GND
VCCENOVP
GBIAS
PWMOUT
PWMOUT
PWMDIM
1
2
GATE
ISW
GND
3
4
ISP
PWMDIM
WQFN-16L 3x3
GBIAS
GATE
ISW
ISP
ISN
2
3
4
5
6
7
VCACTL
SOP-16
13141516
12
NC
11
SS
10
DCTL
17
9
ACTL
8765
VC
ISN
16
GND
15
VCC
14
OVP
13
EN
12
NC
11
SS
10
DCTL
98
DS8452-02C March 2008www.richtek.com
1
RT8452
Typical Application Circuit
V
Analog
Dimming
R1
10k
C2
3nF
R1
10k
C2
3nF
IN
5V
C3
10nF
Figure 1. Analog Dimming in Boost Configuration
V
IN
5V
C3
10nF
C4
4.5V to 40V
4.5V to 40V
PWM
Dimming control
C1
15
13
10
11
C4
C1
C5
0.5uF
9
8
1
15
13
10
8
11
1
9
Conceptual
L
10uH
RT8452
VCC
EN
ACTL
DCTL
VC
SS
GBIAS
VCC
EN
DCTL
VC
SS
GBIAS
ACTL
PWMOUT
PWMDIM
GND
L
10uH
RT8452
PWMOUT
PWMDIM
GND
2
GATE
4
ISW
6
ISP
7
ISN
14
OVP
3
5
16, Exposed Pad (17)
2
GATE
4
ISW
6
ISP
7
ISN
14
OVP
3
5
16, Exposed Pad (17)
R3
R3
C5
1uF
R5
C6
1uF
R5
R4
R4
R2
180mV
R2
180mV
V
V
OUT
OUT
V
OUT
60V MAX
V
OUT
60V MAX
Figure 2. PWM to Analog Dimming in Boost Configuration
V
OUT
V
4.5V to 40V
R1
10k
C2
3nF
5V
L
VCC
EN
ACTL
DCTL
VC
SS
GBIAS
10uH
RT8452
GATE
ISW
ISP
ISN
PWMOUT
PWMDIM
OVP
GND
16, Exposed Pad (17)
14
2
4
6
7
3
5
R3
IN
C1
15
13
9
10
8
11
C3
10nF
1
C4
C5
1uF
R5
180mV
R4
R2
V
OUT
60V MAX
Figure 3. True PWM Dimming in Boost Configuration
DS8452-02C March 2008www.richtek.com
2
Sense Pin. Connect the current
V
4.5V to 40V
IN
5V
Analog
Dimming
R1
10k
C2
3nF
C3
10nF
C1
C4
Figure 4. Analog Dimming in Buck-Boost Configuration
Functional Pin Description
15
13
9
10
8
11
1
Conceptual
RT8452
VCC
EN
ACTL
DCTL
VC
SS
GBIAS
PWMOUT
PWMDIM
GND
L
10uH
2
GATE
4
ISW
7
ISN
6
ISP
3
5
14
OVP
16, Exposed Pad (17)
R3
R5
R4
C5
1uF
R2
180mV
V
OUT
V
OUT
60V MAX
RT8452
SOP-16 QFN3X3-16 Pin Name
Pin Function
1 1 GBIAS The Internal Gate Driver Bias Pin.A good bypass capacitor is required.
2 2 GATE The External MOSFET Switch Gate Driver Output Pin.
3 3 PWMOUT The Output Pin for the PWM Dimming FET Driver.
4 4 ISW
The External MOSFET Switch Current
sense resistor between external N-MOSFET switch and the ground.
5 5 PWMDIM The Control Input Pin for the PWM Dimming FET Driver.
6 6 ISP The LED Current Sense Amplifier Positive Input.
7 7 ISN
The LED Current Sense Amplifier Negative Input. Voltage
threshold between ISP and ISN is 180mV.
8 8 VC The PWM Control Loop Compensation Pin.
9 9 ACTL
The Analog Dimming Control Pin. The effective programming
voltage range of the pin is between 0.3V and 1.2V.
By adding a 0.1uF filtering capacitor on ACTL pin, the PWM dimming
10 10 DCTL
11 11 SS
signal on DCTL pin can be averaged and converted into analog
dimming signal on the ACTL pin following the formula below.
V
= 1.2V x PWM Dimming Duty Cycle.
ACTL
The Soft-Start Pin. A capacitor of at least 10nF is required for proper
soft start.
12 12 NC No Internal Connection.
13 13 EN
14 14 OVP
The Chip Enable (Active High) Pin. When this pin voltage is low, the
chip is in shutdown mode.
The Over Voltage Protection Pin. The PWM converter turns off when
The voltage of the pin goes higher than 1.2V.
15 15 VCC
16
16
Exposed Pad (17)
DS8452-02C March 2008www.richtek.com
GND
The Power Supply Pin of the Chip. For good bypass, a low ESR
Capacitor is required.
The Ground Pin. The exposed pad must be soldered to a large PCB
And connected to GND for maximum power dissipation.
3
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